Dual pump transmission

ABSTRACT

A dual pump apparatus for use on a vehicle or industrial application having a housing in which a pair of hydraulic pumps are mounted, having a cooling fan mounted on the primary or secondary input shaft on the opposite side of the pulley used to engage the prime mover. A charge pump may be mounted on the end cap, and the trunnion arms for controlling the hydraulic pumps extend out of opposite sides of the housing. An auxiliary pump may also be mounted on the primary input shaft and may be located either at the input end thereof adjacent to the pulley, or on the opposite side of the housing.

RELATED APPLICATION

This application claims the benefit of and is a continuation of U.S.application Ser. No. 10/701,830 filed on Nov. 5, 2003 now abandoned,which is a continuation of U.S. application Ser. No. 10/118,263 filed onApr. 8, 2002, which is now U.S. Pat. No. 6,672,843. These applicationsare incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This application relates in general to hydrostatic transmissions and inparticular to a dual pump arrangement. Hydrostatic pumps are well-knownfor use in driving vehicles such as tractors and other off-road devices.Such pumps are also used in a wide variety of industrial applicationsother than vehicles.

In one known arrangement for a vehicle, a plurality of pumps are mountedin separate housings on a vehicle frame. The pumps are each connected toa respective hydrostatic motor through high pressure hoses, which areoften connected to end caps. The end cap is secured to the pump housingand includes a running surface for the pump and porting to connect thepump to the hoses.

A control arm is engaged to each hydrostatic pump to control the outputof the pump. In a known design, the hydrostatic pump is of an axialpiston design and the control arm is engaged to a swash plate, therotation of which can change the output of the pump from forward toneutral to reverse. Rotation of the pumps is provided by rotary inputshafts which are separately driven by the vehicle engine by pulleys andbelts or other known methods. The pump transmits hydraulic fluid throughone of a pair of high pressure hoses to a hydrostatic motor. Rotationaloutput of the motor is then transmitted to the vehicle drive wheelsthrough an output axle or other known means.

Such an arrangement allows for zero turn capability, since thehydrostatic pumps may be operated independently of one another. However,there is a cost involved with this arrangement, as it requires at leastfour separate housings for the individual pumps and motors, and eachhousing must be individually secured to the vehicle frame.

Another known hydrostatic transmission is the BDU transmission. Thishydrostatic transmission comprises a single housing enclosing both ahydrostatic pump and a hydrostatic motor, both of which are mounted to asingle plate. The pump input shaft and motor output shaft are parallelto one another, and the plate contains hydraulic porting to connect thepump and motor. One such hydrostatic transmission is shown in U.S. Pat.No. 5,392,670. Such an HST is generally used to connect to a drive trainfor powering output axles of a tractor or similar vehicle.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a lower cost hydrostaticpump design that can be used in, e.g., a zero turn vehicle, or inindustrial applications. This invention in the preferred embodiment usesa dual pump design having two pumps mounted in a side-by-sidearrangement within a single housing. The housing can include an end capor plate having hydraulic porting therein. High pressure hoses engagedto the end cap or plate are then connected to a plurality of hydrostaticmotors engaged to vehicle drive wheels. Control arms can be mounted onvarious locations on the common housing to independently control thepumps.

A benefit of this design is that it eliminates the need for separatehousings for the two pumps, and reduces the number of mounting pointsrequired on the vehicle. A further advantage is that it eliminates theneed for separate drive inputs for the two pumps. In the preferredembodiment, a single input shaft drives both pumps. This input shaftcould directly drive one pump and be engaged to and drive a second inputshaft for the second pump through gearing which could be either internalor external to the common pump housing. A benefit of this arrangement isreduced cost and size, and the ability to maintain both pumps at aconstant speed.

A key feature of this design is the flexibility it affords to the userof the apparatus. For example, with minimal design changes, one or morecharge pumps and/or auxiliary pumps may be attached to the primary inputshaft or the secondary input shaft as needed to provide charge fluid tothe hydraulic circuit or to power additional units, such as mowers, decklifts, as may be needed.

A further benefit of this design is the ability to use an input shafthaving a varying diameter, which permits the use of, among other things,a more substantial auxiliary pump on this shaft. Another benefit is thelocation of the two trunnion arms to operate the pump swash plates onopposite sides of the pump housing, corresponding to the sides of thevehicle, to avoid clearance problems and to simplify connection of thetrunnions to the control mechanism of the vehicle. Prior art designshave the trunnions extending from one side, corresponding to the frontor back of the vehicle, which thus requires additional linkages to turnthe controls 90 degrees. A further benefit is the use of a single bypassvalve for both pumps and the location of this valve on the side of thehousing which is different from the mounting of the two trunnion arms.

While the preferred embodiment uses a single pump cavity inside thehousing to mount both of the pumps, it is possible to use separatecavities to independently mount the pumps, which would permit varyingpressures to be used for industrial applications and other uses wheresuch different pressures may be important.

Another benefit of this design is the ability to locate a cooling fan onthe top of the unit, with the drive input or primary input shaftentering from the bottom of the unit. This design protects the coolingfan from debris that may be kicked up during operation at the bottom ofthe unit. One could also use a return to neutral mechanism with thisdesign in a known manner, such as that described and shown in co-pendingapplication Ser. No. 09/789,419 entitled “Zero-Turn Transaxle withMounted Return to Neutral Mechanism,” the terms of which areincorporated herein by reference.

Additional benefits and objects of this invention will be apparent tothose of skill in the art from a review of the following description andthe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydraulic schematic of a first embodiment of the presentinvention.

FIG. 2 is a side view of the external casing of a first embodiment ofthis invention.

FIG. 3 is an end view of the dual pump design shown in FIG. 2.

FIG. 4 is a bottom view of the dual pump design shown in FIG. 2, withoutthe input pulley shown for clarity.

FIG. 5 is a top view of the dual pump design shown in FIG. 2.

FIG. 6 is a cut-away side view of the internal components of the dualpump arrangement shown in FIG. 2, along the lines 6—6 in FIG. 5, withcertain parts shown in solid and one of the pumps deleted for clarity.

FIG. 7 is a cross-sectional view of the end cap of a first embodiment,along the lines 7—7 in FIG. 2.

FIG. 8 is a bottom view of a vehicle including a first embodiment of thedual pump apparatus of the present invention.

FIG. 9 is a side view of the vehicle in FIG. 8, with one wheel removedfor clarity.

FIG. 10 is a side view of the dual pump design shown in FIG. 9.

FIG. 11 is a cross sectional side view of a variation on the firstembodiment of this invention, with certain elements shown in solid andthe second pump deleted for clarity.

FIG. 12 is a side view of the external case of a second embodiment ofthe present invention.

FIG. 13 is a top plan view of an end cap in accordance with the secondembodiment of this invention.

FIG. 14 is a cross-sectional top view of the end cap shown in FIG. 13.

FIG. 15 is a cross-sectional side view of the end cap shown in FIG. 13including portions of the pump shafts.

FIG. 16 is a top view of a vehicle showing the dual pump apparatus ofthe second embodiment of this invention.

FIG. 17 is a bottom view of the vehicle shown in FIG. 16.

FIG. 18 is a side view of the external casing of the dual pumparrangement in accordance with the second embodiment of this inventionas shown in FIG. 16.

FIG. 19 is the hydraulic schematic of the second embodiment of thisinvention.

FIG. 20 is an external side view of a third embodiment of thisinvention.

FIG. 21 is a cross sectional top view of the end cap for the embodimentshown in FIG. 20.

FIG. 22 is the hydraulic schematic for the embodiment shown in FIG. 20.

FIG. 23 is a cross sectional side view of a fourth embodiment of thisinvention, again with certain elements shown in solid for clarity.

FIG. 24 is an external side view of a fifth embodiment of thisinvention.

FIG. 25 is an external side view of a sixth embodiment of thisinvention.

FIG. 26 is an external end view of a seventh embodiment of thisinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

The following is a description of the multiple embodiments of thisinvention. Where appropriate, like numerals indicate identical orsubstantially identical components, and similar numerals with adifferent initial numeral indicate similar components with certaindifferences as specified.

The hydraulic schematic of a first embodiment of this dual pump unit 10of the present invention is shown in FIG. 1, while the externalstructure thereof is shown in FIGS. 2–5. The internal structure of dualpump unit 10 of this invention is shown in FIG. 6. While this view is across sectional view, certain elements such as end cap 30, input shaft25, spur gears 52 a and 52 b, and others are not shown in cross-sectionfor purposes of clarity. In addition, while one pump 51 a is shown inFIG. 6, the other pump 51 b is not shown merely for purposes of clarity.The hydraulic porting of end cap 30 is shown in FIG. 7. It will beunderstood that the drawings are not to scale, and the arrangement andsizing of the components will be obvious to a person of skill in theart. The size of pumps 51 a and 51 b and the other components will bedictated primarily by the intended applications of the unit and anyrequired external dimensions.

Inside of housing 20 is located a pump chamber (or cavity) 50 in whichare mounted first rotatable pump 51 a and a second pump 51 b, both ofwhich are rotatably mounted on running surface 31 on end cap 30. End cap30 is secured to housing 20 by means of a plurality of screws 32 andacts in this design to close off the pump chamber 50. The followingdiscussion of pump 51 a will also apply to the second pump 51 b which isnot depicted in FIG. 6 merely for purposes of clarity, but is shown inthe schematic of the system shown in FIG. 1. Pump 51 a is of the axialpiston design and comprises rotatable cylinder block 53, in which aremounted a plurality of axial stick pistons 55, each of which includes apiston spring 56 therein, with cylinder block 53 engaged to first inputshaft 25 by means of spline 44 or similar means. Pistons 55 abut athrust bearing 47 mounted in swash plate 48. Trunnion arm 21 ainterfaces with swashplate 48 through slider bearing 49. Rotation oftrunnion arm 21 a thus moves swash plate 48 and will control thedirection and flow rate of the output of hydraulic pump 51 a. End cap 30is preferably made of aluminum, and pump 51 a runs on a valve plate 57mounted on running surface 31 of end cap 30. Other materials such ascast iron could also be used. Strengthening ribs 46 are also formed onrunning surface 31 to provide additional support, although neither ribs46 nor valve plate 57 are necessarily required.

Trunnion arm 21 a extends out of housing 20 through seal 58 and bushing59. As shown in FIGS. 2 and 3, the two trunnion arms 21 a and 21 b aremounted to separate control arms 22 a and 22 b with set screws 24 a and24 b. Control arms 22 a and 22 b can be engaged to various linkagemechanisms so that the two separate pumps 51 a and 51 b can beindependently controlled by the vehicle operator. The location oftrunnion arms 21 a and 21 b on opposite ends of the housing 20(corresponding to the sides of vehicle frame 88) permits the use of moreefficient linkage systems (not shown).

Input shaft 25 is driven by pulley 27 which is engaged by a belt orother known method to an engine 84, as shown in FIGS. 8 and 9. In thisembodiment, the output of engine 84 is vertical with respect to theground, as are the two input shafts 25 and 26. This arrangement permitsthe use of a cooling fan 19 on the top of housing 20, as shown in FIGS.9 and 10, where it is secured to and driven by the end of input shaft25. This arrangement protects fan 19 from debris that may be kicked upunder the vehicle during operation. Fan 19 could also be mounted toinput shaft 26, which would be extended out of the housing in a similarmanner, such as is shown in FIG. 24.

It should be noted that the extension of input shaft 25 through chargepump cover 35 is optional; shaft 25 need not extend out in such amanner, in which case charge pump cover 35 would be a solid structure onthe top thereof. Input shaft 25 could also be directly driven by engine84, as is shown in FIG. 16 as an alternative embodiment. It will also beunderstood by one of skill in the art that the use of “top” and “bottom”to describe the structures shown in FIGS. 2–10, for example, is forconvenience and relates to the preferred arrangement of these features.As shown elsewhere and as would be understood, this is not limiting onthe manner in which such a pump apparatus 10 could be mounted in avehicle or other structure.

Spur gears 52 a and 52 b, which are preferably helical spur gears, aremounted in gear chamber 45, which may be sealed from pump chamber 50.Spur gear 52 a is mounted on input shaft 25 and is directly engaged tospur gear 52 b, which is mounted on shaft 26, and secured theretothrough a retaining ring 54. Shaft 26 in turn drives second pump 51 b.

Gear chamber 45 is formed by housing 20 and gear cover 41, which issecured to housing 20 through a plurality of screws 43. A sealant wouldpreferably be used at this junction surface to prevent leakage ofhydraulic oil or gear grease. Input shaft 25 is supported in gear cover41 through a retaining ring 61, bearing 62 and seal 63, and pulley 27 issecured to input shaft 25 by means of a standard screw and washer set64. Similarly, input shaft 25 also extends through housing 20 into pumpchamber 50 through bearing 65, washer 66, seal 67, and retaining ring 68to properly locate input shaft 25 and prevent fluid leakage between pumpchamber 50 and gear chamber 45. A similar arrangement would be used withthe interface of second shaft 26 between gear chamber 45 and pumpchamber 50.

As shown most clearly in FIGS. 5 and 6, charge pump 42, which is agerotor style charge pump, is mounted in cover 35 and is splined toinput shaft 25. Charge cover 35 is secured to end cap 30 through aplurality of screws 36 and a seal 37 is used to prevent fluid leakage.

The hydraulic porting in end cap 30 is shown in FIG. 7. System ports 71and 73 extend through the length of end cap 30, with ports 71 a and 73 ain communication with first pump 51 a. A set of check valves 101 a, 101b, 103 a and 103 b are threaded into respective openings in end cap 30,corresponding to ports 71 a, 71 b, 73 a and 73 b. Check valves 101 a,101 b, 103 a and 103 b are of a standard poppet design known in the art,and each includes a bleed 34 formed in the end thereof. Check valves 101a and 103 a are in communication with pump 51 a, while check valves 101b and 103 b are in communication with pump 51 b.

One of ports 71 a or 73 a will be under high pressure when pump 51 a isin stroke and the other port will be under low pressure, or vacuum. Whenswash plate 48 is moved to the neutral position neither port will beunder pressure, and when the direction of swash plate 48 changes (e.g.,from forward to reverse) the status of ports 71 a and 73 a will switch,with the formerly low pressure or vacuum side being placed under highpressure, and vice versa. The ends of each system ports 71 a, 71 b, 73a, and 73 b are threaded to permit connection of the necessary hoses andthe like. Channel 78 is cast into end cap 30 to connect system ports 73a and 73 b, while channel 79 connects system ports 71 a and 71 b.

A further benefit of this design is the use of a single bypass valve forboth pumps. As shown most clearly in FIG. 7, the bypass consists ofvalve body 38 mounted in opening 75, which is bored through end cap 30.Plug 76 is mounted in the opposite end of valve opening 75, and valveactuator 74 is mounted in plug 76 and extends through the length ofopening 75 to extend out of valve body 38. Bypass actuator 74 is shapedso that when the bypass is not activated, it acts to block fluid flowthrough channels 78 and 79 so that the two sides are not in fluidcommunication with one another. Actuator 74 also includes two throats 81a and 81 b each having a cross-drilled hole therein, and a centralpassage 77 formed internally through the body of actuator 74. Whenactuator 74 is depressed, it moves in an axial direction, compressingbypass spring 83, so that throat 81 a is moved into channel 78 andthroat 81 b is moved into channel 79, thus permitting fluid flow intocentral passage 77 and into all four system ports 71 a, 71 b, 73 a and73 b, placing the unit into bypass mode. Throat 81 c is formed on bypassvalve actuator to permit charged oil to flow to check valves 101 b and103 b during normal operation.

FIGS. 8 and 9 depict a vehicle incorporating a first embodiment of thepresent invention. The arrangement shown here is of a rear enginemounting, where engine 84 is mounted on vehicle frame 88, which alsosupports wheel motors 90, mower deck 89 and other possible attachments.Axles 87 extend from wheel motors 90 and drive vehicle wheels 85.

Pump housing 20 is mounted on the top of the vehicle frame 88 in themanner shown so that end cap 30 is on the top of housing 20 and pulley27 is mounted on the bottom thereof. A mounting flange 40 may beintegrally formed with or otherwise attached to housing 20 to secure thepump apparatus 10 to frame 88 in a number of known manners. Belt 69extends from engine 84 to pulley 27 to drive the dual pumps in themanner described herein. Hydraulic high pressure hoses 70 a and 70 bcarry fluid from threaded system ports 71 and 73 to the respective wheelmotors 90. The unit 10 is preferably located along the center line ofthe vehicle, i.e., along the center of the longitudinal axis of thevehicle, as shown in FIG. 8. Unit 10 may be rotated 90 degrees from theorientation shown in FIG. 8, such that the input shafts 25 and 26 arelocated on the vehicle center line in addition to having the unit 10located on the vehicle center line. This location of housing 20simplifies the arrangement and connections of the various hoses, linkagemechanisms and the like. One such advantage is that hoses 70 a and 70 bmay be generally symmetrical in length and routing. This length symmetryincludes having hoses 70 a of one generally identical length and hoses70 b of a second generally identical length, or having hoses 70 a and 70b being of one generally identical length. Note that while theaforementioned discussion relates to the preferable positioning of thepump unit 10 on the vehicle center line, the pump unit may be positionedin other locations as need dictates.

This embodiment includes an external oil reservoir 86 which may bemounted at various locations on the vehicle. Oil drains from pumpchamber 50 through case drain 23, through outlet hose 91 b to thereservoir. Oil returns to the system through inlet hose 91 a, passingthrough filter 92 into charge pump inlet 72. An optional oil cooler (notshown) could also be added to the system and located to take advantageof the air flow from cooling fan 19.

Referring to FIGS. 3 and 7, channel 80 is bored into end cap 30 and issealed at its open end by a cap or plug 33 or similar means. Thelocation of this channel 80 between system ports 71 and 73 allows for anarrower end cap 30 than known designs. Charge pump inlet 72 providesfiltered oil from reservoir 86 through hose 91 a. The opening in whichplug 33 is mounted could also be used as the charge pump inlet fromreservoir 86 as an alternative design. This would eliminate the need forseparate inlet 72, but given the small space around bore 80 on theexternal housing, assembly and maintenance become more complicated withsuch an alternative design.

Kidney 93 provides oil from channel 80 to charge pump 42. Pressurizedoil is sent from charge pump 42 to the system through openings 94.Charge relief opening 97 is also formed in channel 80 to permit oil tobe discharged therethrough in the event of excess oil pressure.

Bearing 95, which is preferably a standard friction bearing, is used notonly to support input shaft 25 but also to divide channel 80 into twoseparate sides, where inlet 72 and kidney 93 which supply oil from thereservoir 86 to charge pump 42 are on one side thereof, and openings 94providing pressurized oil from the charge pump 42 to the system is onthe other side. A similar bearing 96 is also used to support secondshaft 26.

As shown in FIGS. 2 and 10, case drain 23 is located in housing 20 in alocation corresponding to pump chamber 50, so that oil will draindirectly from chamber 50 to reservoir 86, and it will be passed throughfilter 92 before its return to the system. Filter 92 could also belocated on hose 91 b. As noted above, pump chamber 50 and gear chamber45 can be strictly segregated, such that the hydraulic oil used in pumps51 a and 51 b is not used to lubricate spur gears 52 a and 52 b. Thissegregation would permit the use of a gear lubricant in gear chamber 45,which may be desirable in certain applications.

A variation of this design is shown in FIG. 11, and this variation canbe combined with the other embodiments disclosed herein. In thisvariation, the same hydraulic oil is used in both pump chamber 50 andgear chamber 45, with case drain 123 located at the gear cover 41, whichcan otherwise be identical to gear cover 41 shown in FIG. 2. A leakagepath 105 may be formed in housing 20 to permit oil to drain from pumpchamber 50 to gear chamber 45 when the unit 10 is in the standardarrangement as shown in FIG. 11. A benefit of this design is that, dueto its location, gear chamber 45 will generally be cooler than pumpchamber 50, which will assist in the cooling of the hydraulic oil. Thisarrangement will also ensure that any impurities introduced to the oilfrom spur gears 52 a and 52 b will be passed through filter 92 beforebeing returned to the system, which is particularly important if pumpchamber 50 and gear chamber 45 are not strictly segregated.

A further variation on the preferred embodiment is shown in FIG. 26,which includes control arm 104 combined with scissor arms 107 a and 107b and return arms 109 to create a return to neutral feature for thehydraulic pumps 51 a and 51 b. This structure would obviously be used onboth sides of the housing 20. Similarly, friction packs and stops whichhave been used in conjunction with other hydrostatic devices could alsobe used with unit 10.

A second embodiment of the present invention is shown in FIGS. 12–19. Inthis embodiment of pump apparatus 110, the orientation of the swashplates 48 has been changed, which also changes the location of trunnionarms 21 a and 21 b, control arms 22 a and 22 b and output system ports171 a, 171 b, 173 a and 173 b. This alternative arrangement can be usedto accommodate different needs regarding vehicle linkages or othercontrol mechanisms (not shown) that may be secured to pump apparatus110.

As shown in FIGS. 12 and 18, trunnion arms 21 a and 21 b extend from acommon side of the housing 120, instead of from opposite ends as isshown in FIG. 2. This rotation of the orientation of swash plates 48requires a different end cap 130, as shown in FIGS. 13–15. As shown inFIG. 13, pump running surface 131 includes a pair of kidneys 131 a and131 b corresponding to first pump 51 a and a second pair of kidneys 131c and 131 d corresponding to second pump 51 b. The orientation ofkidneys 131 a–d has been rotated ninety degrees from that of the firstembodiment.

FIG. 14 shows a cross-section of end cap 130 along the lines 14—14 inFIG. 12, while FIG. 15 shows a cross-section along the lines 15—15 inFIG. 13. In this embodiment, system ports 173 a and 171 a correspond tokidneys 131 a and 131 b, and ports 171 b and 173 b correspond to kidneys131 c and 131 d. In this embodiment the charge channel comprises aplurality of sections, including sections 180 a, 180 b, 180 c and 180 ddrilled into end cap 130 at right angles to one another, with section180 a capped by plug 133 at its external end and section 180 c capped byplug 133′ at its external end. Fluid enters charge channel 180 d throughinlet 172 which may be connected to the external reservoir 86; as in theprior embodiment, bearing 95 acts to divide channel 180 d into an inletside and an outlet side. Charge pump 42 is mounted in charge housing 35,and oil flows into charge pump 42 through channel 42 a and is returnedunder pressure to channel 180 d through channel 42 b. A charge reliefvalve 99 consisting of a standard check ball and spring design andreturn channel 99′ is used to prevent the charge system pressure fromexceeding design limits. Given the location of system ports 171 a, 171b, 173 a and 173 c on the same side of end cap 130, charge inlet 172 canbe located on the end of end cap 130 instead of the top thereof, withoutconcern for interference with other components as is present in thefirst embodiment.

System ports 173 a and 173 b are also cross-drilled with portions 173 cand 173 d at right angles to primary ports 173 a and 173 b,respectively, for ease of manufacture, with caps 98 used to close theports 173 c and 173 d as needed. This design also permits the insertionof check valves 111 a and 111 b into the internal portion of end cap 130in the manner shown. This arrangement decreases the overall size of theend cap 130 and increases the flexibility of the unit for variousapplications. Check valves 113 a and 113 b are inserted into chargechannel 180 b at respective ends thereof. Having all of the requiredelements located in the same plane also decreases the required thicknessof end cap 130.

This embodiment uses two separate bypass mechanisms which are identicalin construction, and thus only one need to be described. There are anumber of known manners to retain such a bypass mechanism in theactuated mode, such as the use of a detent and/or cotter pins. Withreference to the bypass mechanism on the left side of FIG. 14, it can beseen that a valve opening 175 is bored through a portion of end cap 130,and valve body 138 is mounted at the open end thereof. Valve actuator174 is mounted in opening 175 and extends out of valve body 138; spring183 mounted in the opposite end of opening 175 acts to maintain actuator174 in the position shown in FIG. 14, i.e., the non-bypass or operationposition.

Throats 181 a and 181 b formed in actuator 174 correspond with systemports 173 b and 171 b, respectively, and with open central passage 177,so that when actuator 174 is activated and depressed, ports 173 b and171 b are in fluid communication and thus that side of the unit is inbypass. Similarly, actuation of the other bypass mechanism shown in FIG.14 will place ports 173 a and 171 a in fluid communication, thuscreating a bypass arrangement for the other side.

As shown most clearly in FIGS. 16–18, this arrangement permits the pumpapparatus 110 to be mounted on vehicle frame 88 so that the axes ofpumps 151 a and 151 b are parallel to the longitudinal axis of thevehicle, as opposed to FIG. 8, where these axes are perpendicular to oneanother. This design permits the primary input shaft 25 to be directlydriven by engine shaft 84′, with the two shafts connected by a standardcoupler 82. This eliminates the need for a separate belt and pulley,which decreases costs and increases the efficiency of the unit.Reservoir 86 may be secured to housing flange 140 (or to vehicle frame88) by means of brackets 18 or other known fastening mechanisms and isin communication with case drain 123.

In this design, control arms 22 a and 22 b are mounted on the top sideof housing 120 with respect to vehicle frame 88, which may increase theease of connection with the various linkage mechanisms (not shown),depending on the structure of the vehicle. This arrangement alsosimplifies the connection of the high pressure hydraulic hoses 170 a and170 b from system ports 171 a, 171 b, 173 a and 173 b to wheel motors90, which drive axles 87 and wheels 85.

A further embodiment is shown in FIGS. 20–22, where the primarydistinction from the embodiments described above is the use of twoseparate charge pumps, namely charge pump 242 mounted in cover 235 anddriven by primary input shaft 225, and a second charge pump 242 amounted inside second charge cover 235 a and driven by second inputshaft 226. Both charge covers 235 and 235 a may be mounted on end cap230 in a manner similar to that disclosed above.

End cap 230 shown in FIG. 21 is substantially identical to end cap 30shown in FIG. 7, with the addition of a second charge pump channel 280on the side of end cap 230 opposite to charge channel 80. The design andoperation of charge pump channel 280, bearing 295, inlet 272, kidney293, return openings 294 and charge relief 297 corresponding to secondpump 51 b are generally identical to those features of the correspondingfirst pump 51 a on the opposite side of end cap 230, as described abovewith regard to FIG. 7. The other element of this embodiment, such asbypass actuator 74 and check valves 101 a, 103 a, 101 b and 103 b can beidentical to that described above. As shown in the schematic shown inFIG. 22, the two charge inlets 72 a and 72 b can be fed from a singleinput from filter 92. This design permits use of smaller charge pumpsand a better balance of the charge pressure of the two sides of thecircuit, which may be appropriate for certain applications.

A further embodiment is shown in FIG. 23, wherein the housing 320 ismodified to provide two separate internal pump compartments 350 a and350 b for pumps 51 a and 51 b; both pump 51 a and 51 b having respectivecharge pumps 42 a and 42 b, and the porting and associated structures ofend cap 430 can be identical to that described with respect to FIGS.20–22. Such a design would be preferred in industrial applications,where it is more likely that the different pumps 51 a and 51 b would besubjected to widely varying pressures depending on their uses. Such adesign would require some duplication of components, such as the casedrains, that would be obvious to one of skill in the art.

A unique feature of the present invention is its flexibility in allowingdifferent arrangements of its features. One further embodiment is shownin FIG. 24, where auxiliary pump 106 is mounted on end cap 30′. Thisembodiment is for purposes of illustration otherwise externallyidentical to that shown in FIG. 20. Auxiliary pumps are known for usewith bantam duty pumps and other hydrostatic devices and generally areused to provide hydraulic fluid to power elements such as hydrauliclifts, mower decks, and the like. Auxiliary pump ports 108 a and 108 bare connected to the external apparatus (not shown) to be powered and tothe reservoir, as is known in the art. The internal structure ofauxiliary pump 106 can be one of many designs known in the art for suchuses. In this embodiment shown in FIG. 24, a charge pump (not shown) ismounted within cover 35′ mounted on end cap 30′. The primary internaldistinction from end cap 230 shown in FIG. 20 is that end cap 30′ inFIG. 24 would only need the porting for one charge pump, similar to thedesign shown in FIGS. 1–10. A benefit of this design is that it permitsuse of an auxiliary pump within the same “envelope” as the otherdesigns, thus permitting the user to have this auxiliary pump capacitywithout increasing the overall size of the unit.

A variation of this auxiliary pump design is shown in FIG. 25, where theauxiliary pump 106′ is mounted on the opposite side of dual pump unit10, which for purposes of this illustration is otherwise identical tothe embodiment shown in FIGS. 1–10. As shown most clearly in FIG. 6,input shaft 25 has a first diameter D1 at the first end thereof where itis engaged to pulley 27 and spur gear 52 a. The diameter is reduced atthe point where input shaft 25 extends into pump chamber 50 to D2. Inthe preferred embodiment, D2 is approximately 0.625 in. and D1 isapproximately 0.82 in. for a standard application, assuming a 16 HP peakinput to each pump 51 and 5 HP input to the auxiliary pump 106′. Theproper size of these diameters will depend on the torque needs of thehydraulic pumps and auxiliary pump used with the design and can bereadily calculated by one of ordinary skill in the art. Input shaft 25′shown in FIG. 25 differs from input shaft 25 shown in FIG. 6 in theaddition of a spline or other engagement means (not shown) to engageauxiliary pump 106′. This arrangement permits the use of a standard sizepump 51 a, which requires a standard size shaft while still using alarger diameter D1 to drive spur gear 52 a. This portion of input shaft25′ having larger diameter D1 extending out of gear cover 41 alsopermits the use of a much larger auxiliary pump 106 than would otherwisebe possible if input shaft had a constant diameter.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangement disclosed is meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any equivalents thereof.

1. A hydraulic apparatus comprising: a hydraulic mounting member havinga first end, a second end formed opposite the first end and a pair ofsides connecting the first and second ends; a first hydraulic pump and asecond hydraulic pump both rotatably mounted on the hydraulic mountingmember; and a pair of system passages formed in and extending throughthe hydraulic mounting member from the first end to the second end, eachsystem passage comprising a first port in fluid communication with thefirst hydraulic pump and an opening on the first end of the hydraulicmounting member and a second port in fluid communication with the secondhydraulic pump and an opening on the second end of the hydraulicmounting member.
 2. The hydraulic apparatus of claim 1, furthercomprising a bypass valve passage extending into one of the sides of thehydraulic mounting member generally perpendicular to the pair of systempassages and intersecting both of the pair of system passages; and abypass valve located in the bypass valve passage.
 3. The hydraulicapparatus of claim 2, further comprising: a gallery located in thehydraulic mounting member between the pair of system passages; and afirst pair of check valves located on one of the sides of the hydraulicmounting member and a second pair of check valves located on the otherside of the hydraulic mounting member generally opposite the first side,wherein one of the check valves in each pair of check valves is locatedon an opposite side of the bypass valve from the other of the checkvalves.
 4. The hydraulic apparatus of claim 3, wherein the bypass valvepassage is generally located at the midpoint of one of the sides of thehydraulic mounting member between the first end and the second endthereof.
 5. The hydraulic apparatus of claim 2, wherein the bypass valvecomprises a plurality of flow passages formed therein, whereby when thebypass valve is actuated fluid is provided a route to flow from bothsystem passages into the bypass valve passage.
 6. The hydraulicapparatus of claim 5, wherein the flow passages hydraulically connectboth system passages when the bypass valve is actuated.
 7. The hydraulicapparatus of claim 2, wherein each system passage comprises a channelportion connecting the first port to the second port, wherein thediameter of the channel portion is smaller than the diameter of thefirst and second ports.
 8. The hydraulic apparatus of claim 7, whereinthe bypass valve passage intersects both channel portions.
 9. Thehydraulic apparatus of claim 2, wherein the bypass valve passageintersects the first system passage and the second system passage sothat each system passage is separated into two generally equal portions.10. A hydraulic apparatus comprising: a hydraulic mounting member havinga width and a length; at least two pump running surfaces on thehydraulic mounting member; a pair of hydraulic system passages formedin, and extending the length of, the hydraulic mounting member; a bypassvalve passage formed in the hydraulic mounting member near the center ofthe hydraulic mounting member length, the bypass valve passage extendinggenerally perpendicular to and intersecting both of the system passages,whereby the bypass valve passage separates each of the system passagesinto two port portions; and a bypass valve located in the bypass valvepassage.
 11. The hydraulic apparatus of claim 10, further comprising agallery passage formed in the hydraulic mounting member generallyparallel to and located between the pair of system passages; and aplurality of check valves located in the hydraulic mounting member,wherein at least one check valve of the plurality of check valvesoperatively connects the gallery and each of the port portions.
 12. Thehydraulic apparatus of claim 11, wherein the gallery contains an inletto receive fluid from a charge pump and a relief passage to allow excessfluid to escape from the gallery.
 13. The hydraulic apparatus of claim11, wherein the bypass valve extends through the gallery and a fluidpath is formed around the bypass valve at the location where the bypassvalve extends through the gallery.
 14. The hydraulic apparatus of claim11, wherein each check valve is spring biased to a closed position. 15.The hydraulic apparatus of claim 11, wherein at least one of the checkvalves comprises a bleed extending between the gallery and a portportion.
 16. A hydraulic apparatus comprising: a hydraulic mountingmember having a first end, a second end formed opposite the first endand a pair of sides connecting the first and second ends; a firsthydraulic pump and a second hydraulic pump both rotatably mounted on themounting member; and a first pair of system ports open on the first endof the mounting member and in fluid communication with the firsthydraulic pump; a second pair of system ports open on the second end ofthe mounting member and in fluid communication with the second hydraulicpump; a gallery located in the mounting member between the two ports ineither the first pair of system ports or the second pair of systemports; and a first pair of check valves located on one of the sides ofthe mounting member, and a second pair of check valves located on theother side of the mounting member, wherein one of each pair of checkvalves is in fluid communication with one of the first pair of systemports and the other of each pair of check valves is in fluidcommunication with one of the second pair of system ports.
 17. Thehydraulic apparatus of claim 16, further comprising a first channelformed in the mounting member between one of the first pair of systemports and one of the second pair of system ports, and a second channelformed in the mounting member between the other of the first pair ofsystem ports and the other of the second pair of system ports.
 18. Ahydraulic apparatus comprising: a hydraulic mounting member having afirst end, a second end formed opposite the first end and a pair ofsides connecting the first and second ends; a first hydraulic pump and asecond hydraulic pump both rotatably mounted on the mounting member; anda first pair of system ports open on the first end of the mountingmember and in fluid communication with the first hydraulic pump; asecond pair of system ports open on the second end of the mountingmember and in fluid communication with the second hydraulic pump; agallery located in the mounting member; and a first pair of check valveslocated on one of the sides of the mounting member, and a second pair ofcheck valves located on the other side of the mounting member, whereinone of each pair of check valves is in fluid communication with one ofthe first pair of system ports and the other of each pair of checkvalves is in fluid communication with one of the second pair of systemports.
 19. The hydraulic apparatus of claim 18, further comprising abypass valve passage extending into one of the sides of the mountingmember generally perpendicular to both the first and second pairs ofsystem ports, and a bypass valve located in the bypass valve passage.20. The hydraulic apparatus of claim 19, wherein the first check valvein each pair of check valves is located on an opposite side of thebypass valve from the second check valve in each pair.
 21. The hydraulicapparatus of claim 18, wherein the gallery contains an inlet to receivefluid from a charge pump and a relief passage to allow excess fluid toescape from the gallery.
 22. The hydraulic apparatus of claim 18,further comprising a first channel formed in the mounting member betweenone of the first pair of system ports and one of the second pair ofsystem ports, and a second channel formed in the mounting member betweenthe other of the first pair of system ports and the other of the secondpair of system ports.
 23. The hydraulic apparatus of claim 1, furthercomprising a pair of valve plates, each valve plate disposed between oneof the hydraulic pumps and the hydraulic mounting member.
 24. Thehydraulic apparatus of claim 18, further comprising a pair of valveplates, each valve plate disposed between one of the hydraulic pumps andthe mounting member.